Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 101329
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
429 AM AKST Sat Dec 10 2016

.ANALYSIS AND UPPER LEVELS...
The remnants of the low complex that brought snow to much of the
south Mainland on Friday is continuing to move south of the area
as it dissipates, leaving clearing skies and gusty offshore flow
in its wake. These offshore winds are being enhanced by a
shortwave stretching from the north Gulf into Southcentral,
helping to bring bringing gusty winds from the Matanuska River
Valley eastward into Valdez and Thompson Pass. These winds will
all begin to weaken this morning as the shortwave dissipates as it
moves to the south. Behind this shortwave, high pressure from the
interior is beginning to descend into the southern Mainland
allowing for clear and cold conditions to develop over many
interior locations. High pressure continues over the eastern
Bering as well, forcing the front from yet another low near the
western Aleutians to remain confined to the western-half of the
Bering.

&&

.MODEL DISCUSSION...
The models remain in very good synoptic agreement through the
weekend, and have now come into much better agreement with the
speed of the next front the move into the eastern Bering late this
weekend. As a result the higher resolution NAM was preferred to
fine tune gap winds along the Gulf Coast this weekend, with a
little GFS over the Bering to handle some small differences in the
frontal timing. Overall forecast confidence is very good into
early next week.

&&

.AVIATION...
PANC...VFR conditions will persist today with light/variable winds
becoming N-NE up to 10 kt later this morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

A potent upper level trough can be see quite clearly on water
vapor this morning as it pushes southward from the Southcentral
mainland into the Gulf of Alaska. This trough has significantly
weakened the gusty winds in Valdez overnight, as column wind
direction shifted to an unfavorable coast parallel direction, and
also static stability have changed mountain wave dynamics.
Meanwhile, surface pressure gradients across the coast have
remained fairly steady, with fairly steady winds across Thompson
Pass all night. In contrast, this wind direction shift has
further enhanced gusty gap winds across the Matanuska Valley. The
sounding for Anchorage this morning shows this dramatic shift with
drying throughout the column as well. These gusty winds across
Southcentral will slowly relax through Sunday, as the trough
continues to slides towards the north Pacific, and broad high
pressure becomes established. Behind the trough, a much more
benign weather pattern will settle in with no precipitation
expected in the short term. &&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The Aleutian Range will have a few lingering snow showers this
morning as the Low pressure system just south of Kodiak Island
tracks farther eastward. Meanwhile, high pressure continues to
dominate over the North Slope area resulting in offshore
northerly winds through the Southwest Alaska region. Therefore,
look for cooler air to persist through majority of the weekend.
By Sunday afternoon a weather front approaches the Southwest
coastline. This results in the winds shifting to southeasterly
direction, and starts bringing in warmer temperatures to the
region.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The central/eastern Bering remains under northerly flow with cold
air from the north filtering into the region. This will keep
scattered snow showers along the Eastern Aleutians through
Saturday before the wind direction shifts to southeasterly going
into Sunday. This is resulting from an upstream weather front
draping over the western Bering eastward into the Central
Aleutians. This synoptic feature moves farther north into the
central/eastern Bering by Sunday afternoon. Look for the Bering
Sea/Aleutians to have warmer temperatures through the weekend as
this front moves through the region. Therefore, rain/rain showers
accompanies the warmer temperature, but will change to wintry mix
as you go farther north in Bering with the colder temperatures in
place.

&&

.LONG TERM FORECAST (Days 3 through 7...Fri through Tue)...

Sunday evening and beyond, a weakening front over the Eastern
Bering Sea will move into Southwest Alaska before falling apart
as the strong ridge over Southcentral shears it apart. Thereafter,
a series of strong storms look poised to move through the Bering
Sea beginning Monday night. By Wednesday, there is uncertainty
with how strong the ridge over mainland Alaska will be as these
Bering storms attempt to shift the ridging eastward. The ECMWF is
an outlier which holds a much stronger ridge in place, keeping
most of Southern Alaska dry until late in the week. The Canadian
GDPS and GFS are more bullish in sending energetic waves over the
top of the ridge by Wednesday night. For now, an ensemble approach
favoring a shifting ridge axis was preferred which will begin to
highlight precipitation chances by late midweek into the weekend.
This pattern will dramatically shift the sensible weather as
clouds and moisture will likely result in warming
temperatures...along with the threat for snow turning to rain/snow
by the weekend as the Northeast Pacific ridge expands.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 127 128 175 176 177 178.
         Heavy Freezing Spray 126 127 180 181 185.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...JA/TP



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